The forming of 3-dimensional structures has various applications. These applications include large scale applications such as rapid prototyping and layered manufacturing techniques. Conversely, these applications include small scale applications such as semiconductor manufacturing and micro-electromechanical-machines.
The complex manufacture of systems often requires the very expensive machining, tooling, and fastening of individual parts to form a complex structure. Additionally, the labor involved in these processes is both time consuming and expensive. Furthermore, when these complex structures are created and fastened together, every time a fastener is placed into an object, stress analysis must be performed to ensure that the performance of the part is not degraded by the attachment of the fastener. These complex structures require complex analysis to protect and determine their performance in actual conditions and actual use. The simpler a structure becomes the more easily such a structure may be analyzed and models developed to predict the structure's behavior.
Large scale forming of 3-dimensional structures such as rapid prototyping may take many of various forms. Many typical rapid prototyping techniques involve layered manufacturing techniques for technologies. These techniques often build parts on a layer-by-layer basis. Examples of these techniques include stereo lithography, solid ground curing, selective laser sintering, laminated object manufacturing.
Stereolithography has been previously used to generate three-dimensional prototype parts. Stereolithography allows the formation of parts from CAD-generated solid or surface models. The process of making tooling from original conception through all of the required necessary phases prior to implementation in a manufacturing environment is both time consuming and costly. Since the amount of time that it takes to actually reach the production/manufacturing phase of a product can be directly measured in dollars and cents, reducing this time makes the manufacturing process both more efficient and more profitable. CAD software is used as a method to define both the geometry and dimensional requirements of parts. Historically the data from a CAD file may be electronically transmitted to a stereolithography system. There are several different types of stereolithography systems available, each utilizing its own distinct process depending on such factors as the required model accuracy, equipment costs, model material, type of model, and probably most important, the modeling time. One such stereolithography apparatus consists of a vat of liquid polymer in which there is a movable elevator table/platform capable of moving (lowering) in very precise increments depending on the requirements defined by the type of model that is to be constructed. This system may use a helium/cadmium laser to generate a small but intense-spot of ultraviolet light, which is used to scan across the top of the vat of liquid polymer. This scan is controlled by a computer controlled optical scanning system. At the point where the laser and the liquid polymer come into contact, the polymer is fused into a solid by crosslinking. As the laser beam is scanned across an x-y surface, the model is formed as a plastic object, point by point and layer by layer.
However, the accuracy of the model is limited by the type of photopolymer that is being used and the striations associated with the depth of each layer. As each layer is formed, the elevator platform is then lowered so that the next layer can be scanned. As each additional layer is formed, it then bonds to the previous one and the resulting object is generated by a precise number of successive layers.
At the end of this process, the object can then be removed from the support structure and finished by any number of methods until the surface finish is of the texture that is required. Also, the object can then be used as either a negative or a positive mold from which tooling could be formed.
The disadvantage with stereolithography is twofold. First, stereolithography requires the laser to be scanned. Thus, the three-dimensional object is formed layer by layer and point by point. This scanning process can be time consuming. Secondly, stereolithography has been used on plastic material that is easily modified with ultraviolet light. Typically in such a system, the resulting part is brittle and has very little strength.
Similarly, solid ground curing generally involves using a photopolymer sensitive to UV light. It is, however significantly different from stereolithography. Solid ground curing involves moving a manufactured part from various workstations. In one workstation, the photopolymer is exposed to UV light. The UV light is projected through a mask. In this manner, an entire layer is formed at once. Once the layer has been exposed, the uncured areas filled with residual liquid polymer are replaced by wax. The wax is hardened by a cold metal plate and subsequently the layer is milled to the correct height. The milling station also allows for layers to be removed or undone. Then a new layer of polymer is applied and the part is exposed again to UV light projected through a mask.
Similar to stereo lithography, solid ground curing is often limited to photopolymers. In addition both stereolithography and solid ground curing produce parts with striation associated with the layer-by-layer processing.
One process that has been considered to bring rapid prototyping closer to the idea of actually making parts is laser sintering where one actually deposits the material and then the material is sintered so that one can make a part. In laser sintering, a polymer powder, a ceramic powder, or other materials are spread over the platform. A laser sinters selected areas causing the particles to bond together. In some typical applications, a coated ceramic particle is heated with the laser. The coating melts. As the coating cools, the particles bind together.
Selective laser sintering involves two phase transitions. One from solid to liquid and then back to solid again. In many typical applications, laser sintering involves directing a laser across the area. As such, similar limitations apply as those of stereolithography.
Another technique is that of laminated object manufacturing. In laminated object manufacturing, a foil with an undersurface having a binder is pressed and heated by a roller. The foils is rolled across a previous foil The foil is cut by a laser following the contour of the layer or slice.
To more easily remove the excess material, the exterior of the slice is hatched. This hatching is necessary as the layers are solid. Unlike the fluid based processes, excess material is more difficult to remove. Similar to the processes above, the laminated object manufacturing process is limited by the materials that can be used and by the layer limitations described above.
Each of these layered manufacturing techniques is limited by the materials, layered striations and the accuracy with which they can reproduce an object. Because the techniques involve layering material on top of other layers, the accuracy is limited to the layer of thickness. Often these techniques produce striated objects.
Turning to small scale processes, one process for producing a 3-dimensional structure is photolithography. Photolithography is often used in the manufacturing of semiconductors.
In one typical example of photolithography, wafers of silicon are chemically cleaned to remove particulate matter on the surfaces. After cleaning, a barrier layer, typically silicon dioxide is deposited. A photo resist layer is then applied to the surface. Then, the photo resist is exposed to UV light. The UV light is directed through a mask giving it a pattern. Upon exposure, areas of the photo resist become selectively soluble or resistant to development. In development, less resistant regions of the photo resist are dissolved. This leaves an area in which further deposition of silicon dioxide or metallic compounds may be achieved.
One difficulty with the photolithography process is found in mask alignment. To build a series of 3-dimensional structures, mask must be aligned very carefully. Often the ability to align the masks limits the size of the feature being deposited. Further, the photolithography process involves many steps. These steps require the removal of the wafer from the vessel.
Further, these steps require various and diverse processes including deposition, cleaning, baking, chemical dissolving and others. In many typical applications, these steps and processes require the removal of the wafer from the deposition vessel or chamber. This movement of the wafer exacerbates the problem of aligning the mask. In addition, it increases the time required for the manufacturing of the semiconductor chips.
As such, many typical techniques for forming 3-dimensional structures suffer from deficiencies in producing accurate models and/or excesses in costly tooling or method steps. Many other problems and disadvantages of the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.